Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore to the surface. These fluids are generally liquids made up of produced liquid hydrocarbon and often water. One type of system used in this application employs an electrical submersible pump (“ESP”) system. ESP systems include a pump operated by an electrically powered motor for pressurizing the fluid. Pressurized fluid is discharged from the pump and into production tubing, or by other means, for conveyance to surface.
The types of ESP systems in wellbores generally include centrifugal pumps, progressive cavity pumps, reciprocating pumps, and positive displacement pumps. Centrifugal and progressive cavity pumps are usually equipped with a rotating impeller or helical rotor to urge the fluid from downhole to the surface. The reciprocating pumps and positive displacement pumps typically operate by reciprocating a plunger to force wellbore liquid up hole. In any of these designs, vapor lock can occur within the pump when a sufficient amount of gas accompanies the liquid, so that forces applied to the liquid merely compress the gas rather than causing the fluid to be lifted to surface.